Automatic exposure control (AEC) is used in x-ray imaging for exposure management. The goal of AEC is to maintain image quality by delivering appropriate dose to the image detector while minimizing exposure on the patient. In conventional AEC methods, ion chambers or an array of semiconductor diodes are used to provide output signal in real time while the radiation dose is being delivered. Once a given threshold is reached, the exposure is terminated, typically via separate wiring to the x-ray source generator. The x-ray source generator typical has special dose integration electronics built in.
The conventional AEC methods require additional hardware such as AEC ion chambers or an array of semiconductor diodes and readout electronics etc. Very often, multiple AEC chambers are built in, and depending on the imaging setup one or more chambers are selected for exposure control. When in use, the AEC ion chambers are required to be placed at correct locations. Further, in cases where the AEC ion chambers are placed behind the image detector, low remaining radiation is available for the AEC ion chambers and thus low output signals because the image detector typically absorbs up to 70% of the radiation signal. If the AEC ion chambers are placed in front of the image detector when in use, some radiation which would otherwise contribute to image signals in the image detector would be attenuated.
It would be desirable to use the image detector itself to sense the exposure and provide AEC signals in real time without the use of additional AEC ion chambers. Flat panel image detectors are dose responsive and charge integrating devices. The signals that are captured by the image detector are only known after the exposure and the readout of the detector. Conventional flat panel detectors are generally designed to read out signals on a row-by-row or frame-by-frame basis, and not in real time.
Accordingly, there is a general need for an AEC method without the use of external AEC ion chambers or other measuring devices. There is a need for an imaging apparatus or system that incorporates an exposure dose integrating or measuring device or function for automatic exposure control.